Studies on the metabolism of properdin and C3 in patients with rheumatic diseases and biliary cirrhosis are being carried out to determine the clinical significance of activation of the classical and alternative pathway and the genetic control of the synthesis of properdin. Serial biopsies of nonlesional skin in patients with rheumatic diseases are being carried out in order to determine the clinical, prognostic, and diagnostic significance of the presence of IgG, IgM, IgA, C3, C4, Clq and properdin in the dermal-epidermal junction. In SLE patients with nephritis, a study of the dermal-epidermal and glomerular deposition of the subclasses of IgG and the IgG subclass of circulating anti-DNA antibodies is being carried out. High levels of properdin have been demonstrated in the blood relatives of discoid lupus patients who have elevated serum properdin levels. The synthetic rate of properdin appears to be increased in some individuals with elevated serum properdin levels.